This video is sponsored by Magellan TV. Welcome back to Launch Pad, I'm Christian
Ready your friendly neighborhood astronomer. And as you may have heard, the Arecibo radio
telescope collapsed on December 1st, 2020 after 57 years of operation. At a whopping
306 meters - 1000 feet across - it was the largest single-aperture telescope in the world
for most of its life. In fact, it wasn't until 2016 when China's 500-meter Aperture Spherical
Telescope - or FAST - finally broke Arecibo's aperture record. But unlike most radio telescopes, Arecibo
was equipped with a radar. That allowed the telescope to work in reverse and bounce radio
signals off of planets and asteroids and analyze what came back. That allowed Arecibo to discover that Mercury
wasn't tidally locked to the Sun as previously thought, but instead orbits the Sun in a 3:2
spin resonance. Later, it was used to make radar maps of asteroids,
such as Bennu. These observations helped to plan ahead for OSIRIS-REx's mission to capture
a sample. But the most extraordinary use of Arecibo's
radar was back in 1974, when it transmitted a message, announcing humanity's existence
in the cosmos. Even though it's racing away from our solar system at the speed of light,
it won't reach its destination for at least another 22 thousand years. So, while we're waiting for a reply, I thought
we'd talk about the story of the Arecibo message, decode it, and discuss its potential implications.
But first, I'd like to thank Magellan TV, who are very kindly sponsoring today's video. Magellan is a documentary streaming service
featuring content on History, Art, Nature, and of course, Space and Science. Their series on Exploring Venus delves into
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on Roku, AmazonFireTV, AppleTV, Google Play, and iOS. If you enjoy the content here on Launch Pad
Astronomy, then I think you’ll enjoy MagellanTV. That’s why I’m delighted to tell you about
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month of MagellanTV absolutely FREE. Please make sure to use the link in the description
of this video. In 1974, the Arecibo telescope was upgraded
just in time for its 10th anniversary. Astronomer Frank Drake thought to commemorate the occasion
by using Arecibo's radar to send a message to an extraterrestrial civilization. Drake pioneered the Search for Extraterrestrial
Intelligence, or SETI, and is the author of the famous Drake Equation which aims to describe
the number of detectable civilizations within our Galaxy. He collaborated with Carl Sagan
in designing the plaques on the Pioneer spacecraft, and oversaw the creation of the Golden Records
on Voyager. Now, like the Pioneer plaques and Voyager
records, the Arecibo message was a symbolic gesture; it was designed to show that we could
do it and to show off the incredible power of the Arecibo telescope. However, it was also an opportunity to really
think about how to actually construct a message that could be interpreted without any expectation
of a common spoken language. Drake designed the message with the assistance
of scientists at Cornell University as well as Arecibo. Now despite popular myth, Carl
Sagan wasn't involved in helping to design the message, though he certainly supported
and helped promote the effort. And so, on November 16 1974, a message was
beamed to the globular cluster M13. It consists of roughly 100,000 stars and lies
about 22 thousand light-years away in the constellation Hercules. It was chosen because
they wanted the message to reach as many stars as possible. Ideally, they would have sent
the message to the Galactic center. Had that been the case, the signal could have been
intercepted by at least a billion stars, but the Galactic center never rises overhead at
Arecibo's latitude in Puerto Rico. So, M13 was selected instead. The message was sent with Arecibo's megawatt
transmitter. A megawatt of energy isn't a lot if it's omnidirectional; that is, if it
radiates in all directions. But when concentrated into a narrow beam, it outshines the Sun by
a factor of a million! That's powerful enough to be detected by another Arecibo-sized antenna
on the other side of the Galaxy! Now, there's no reason to assume that an alien
civilization would have the same concepts of language as we do. But Drake was confident
that anyone intelligent enough to receive the message would, by necessity, have to have
an understanding of mathematics and science. That's why the signal was broadcast at a frequency
of 2,380 MHz with occasional pulses shifted by 10 MHz. Digitizing the signal produces a string of
bits with two different values. By convention, we treat each bit as either a 1 or 0 but they
could just as easily be either an "on" or "off", whites and blacks, or...whatever
these are. The message was 1679 bits in length. That's
a special kind of number called a semi-prime. that means it can be factored into two prime
numbers. In particular, 1679 factors into the primes 73 and 23. If the bits are arranged
into 23 rows and 73 columns, the message is completely unintelligible. But if is instead
arranged into 73 rows and 23 columns, an unmistakeable message emerges. The message is broken down into seven parts.
The top part of the message are the binary representations of the numbers 1-10. It's
meant to act as a kind of rosetta stone for the rest of the message. Now if you already know how binary works or
don't care to know how binary works, feel free to skip ahead to the next part of the
video. Otherwise, let's walk through how to read the first 10 numbers. The bits at very bottom of each number are
intended as markers to indicate the start of the column for the number in question.
Each bit in the column above represents an increasing power of 2, starting from 0 and
counting upwards. The value of the number the bits represent
is calculated by adding up the values of the bits that are switched on. So for example, in the first column, the bit
above the marker is "on", but the rest are off, so the value of this column is 1 + 0
+ 0, or 1. In the next column, the bottom bit is off
but the one above it is on, followed by a bit turned off, so it's 0 + 2+ 0, or 2. The third number is 1+ 2 + 0, or 3. Four is simply 4. Five is 1+0+4. Six is 0+2+4, and seven is
1+2+4 The numbers 8-10 are a little tricker, because
only the first four rows could be used to express these first 10 numbers, so these numbers
are represented by two columns. This is why the bottom marker is there to indicate where
to start reading the numbers from. So the positions represent 1, 2, 4 as above, followed
by positions 8, 16, and 32. Now writing numbers this way may not be obvious
to anyone who manages to arrange the message correctly, even if they understand binary.
But if they do figure this part out, there's a good chance they can figure out the rest
of the message. The next set of numbers are 1, 6, 7, 8, and
15. These are the atomic numbers of hydrogen, carbon, nitrogen, oxygen, and phosphorous.
These are the elements that ultimately make up DNA. The chemical groups that make up DNA nucleotides
are defined using the same convention. So, for example, 7 hydrogen atoms, 5 carbon
atoms, 0 nitrogen, 1 oxygen, and 0 phosphate atoms form the compound Deoxyribose - the
"D" in "DNA". This is followed by descriptions of Adenine,
Thymine, and Deoxyribose Then two phosphate molecules are presented
on either side of the message, representing their locations on the sides of the DNA double
helix. Then a row of Deoxyribose, Cytosine, Guanine,
and Deoxyribose, Followed by another set of Phosphates. The long double column underneath represents
the number 4 billion, 294 million, 441 thousand, 822. In 1974, this was thought to be the number
of nucleotide base pairs in the human genome. Today, we know that number is closer to 3.2
billion. Oops. Surrounding this number is a graphical representation
of a double helix. Hopefully, whomever receives the message will recognize the shape and understand
that the message is trying to convey DNA information. The double helix converges onto a depiction
of a human being. This could be the most recognizable part of the entire message, assuming whomever
receives it is bipedal. On the left is a horizontal binary depiction
of the number 14. This number, multiplied by the wavelength of the message (126 mm),
gives the height of the average American male. For example, the wavelength of the message
is 126 mm. Multiplied by 14 gives 1.764 meters or 5 feet, 9.4 inches or...whatever units
the aliens would like to measure with. To indicate that this number represents height,
vertical bars appear above and below this number. I admit, I wouldn't have guessed this
one, either. On the right is the binary representation
of the number 4,292,853,750 which at the time was the best estimate of the number of human
beings on planet Earth. The next section represents the solar system,
with the third planet from the Sun raised to indicate where the message came from. And
yes, Pluto is included here as well because at the time, we didn't know there was a larger
Kuiper belt out there. Below that is a graphical depiction of the
Arecibo dish, with a large "M" depicting the path of the radio beam going from the transmitter
to the dish and out into space. Underneath is a the binary expression of the
number 2,430. When this number is multiplied by the wavelength of the message, the telescope's
diameter is revealed. Horizontal dots on either side of the number hint that this number is
used to describe the telescope's diameter. Now, would anyone be able to actually decode
this? Well, the story goes that Drake anonymously mailed an early version of the message to
several scientists around the world. He sent each of them a single piece of paper that
only had a string of 1’s and 0’s printed on it. The paper arrived in an otherwise unmarked
envelope, with no explanation or instructions of any kind. However, every single recipient
managed to decode the string into the message! After Drake constructed the final Arecibo
message, he showed the decoded version to several scientists and asked them to interpret
it. He found that nobody could interpret the entire message. But each scientist recognized
the part relevant to their discipline. In a 2007 interview with Astrobiology magazine,
Drake said that Carl Sagan got the numbers and planetary information correct, but didn't
figure out the DNA chemistry. So who knows? Maybe if the receiving civilization
has enough subject matter experts looking at it, they'll eventually be able to figure
it out. However, it's hard to imagine there's anyone
in M13 to read the message. M13 is a globular cluster made of older stars that formed when
the Universe was much younger. As a result, they don't possess a high abundance of the
heavy elements needed to form complex life. Besides, the radiation environment in a globular
cluster is pretty nasty, so even simple life wouldn't have the best shot at evolving into
something more complex. However, a reply mysteriously appeared in
a crop circle next to the Chilbolton radio telescope in 2001. Now, I'm not saying it's
artists...but it's artists. Of course, the Arecibo message sparked a debate
as to whether or not it's a good idea to directly message aliens to begin with. After all, what
if an alien civilization interprets our message as hostile or worse, they recognize it as
friendly but choose to mount an invasion to enslave us? Personally, I'm really not losing
any sleep over it. I mean, M13 is 22 thousand light-years away. The earliest we could anticipate
a reply is 44 thousand years from now. So I'm sure by then we'll have figured out a
way to hold Charleston. Besides, if they do try to respond, they might
find it increasingly hard to find us. We used to broadcast signals into space all the time.
The surface of our planet was covered with omnidirectional TV transmitters. Each transmitter
broadcast with up to 10 megawatts of power, with as much as half its energy escaping into
space. But now the majority of our transmissions
come from satellites sending narrow beams to the ground. Instead of megawatt transmitters,
a typical satellite sends HBO to the ground at just 20 watts. Less than a single watt
escapes into space at any given time. Maybe that's why we haven't detected any extraterrestrial
signals. Maybe they all got cable and stopped broadcasting. Or maybe they know we're here but they're
leaving us alone following a kind of Prime Directive. Or...maybe we're alone. In any event, we won't be sending another
message with Arecibo. It's destroyed and I have no idea if it will ever be rebuilt. But
that one message will continue to M13 and far beyond. It's interesting to think that
in a way, Arecibo's ultimate legacy will continue to propagate through the Universe long after
we're gone. Meanwhile, the Breakthrough Listen project
may - and this is a big "may", mind you - may have detected a signal that seems to be coming
from somewhere in the region around Proxima Centauri. Now, I'm not holding my breath,
it may turn out to nevertheless be a step forward in the search for techno-signatures. We're
still waiting for the science team to publish their results, I made a video about what we
do know about it so far, so if you haven't seen it yet, I'll see you over there when
we're done here. My thanks as always to my Patreon supporters
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